The use of antibodies to tumor markers as a means of detecting or treating cancers has been attempted many times in the past with varying degrees of success. All the projects which have met with some success essentially have employed antibodies as a carrier for radioisotopes or cytotoxic drugs (i.e., chlorambucil). There have been several problems with all these attempts: non-specificity of the tumor antigen; the inability to purify the antigen; the inability to purify the antibody; and the need for xenogenic antibody. The only way ideally to evaluate tissue or tumor specific antibodies as a means to diagnose or treat tumors would be by using homologous highly specific antibodies which could be purified in sufficient quantities as carriers for isotopes or chlorambucil. Thyroglobulin is found only in thyroid tissue, thyroid cancer and sometimes in embryonic tissues which produce thyroid elements. In the athyroid animal or human it is a specific marker for recurrent or residual thyroid cancer. Thyroglobulin is easily purified, highly antigenic and homologous antibodies to it are easily purified from animals with experimentally induced thyroiditis. Homologus antibodies occur naturally in humans with Hashimoto's disease. We plan to use antibodies to thyroglobulin to deliver isotopes and/or drugs to the thyroid gland and to transplantable thyroglobulin-producing tissue with monospecific purified antibodies in animals, then ultimately we could treat patients with metastatic thyroid cancers. Ninety percent of these tumors produce thyroglobulin and greater than 60% of these do not concentrate iodine. This would provide a method of treatment for patients whose tumors do not concentrate iodine and for whom we currently have no satisfactory method of therapy. This technique would also be applicable to radioscanning for residual disease or other endocrine tissues.